1. Field of the Invention
The present invention relates to a slip control for a motor vehicle. More particularly, it relates to an acceleration slip control system for a motor vehicle which suppresses a slip arising in the driving wheel of the motor vehicle during the acceleration thereof.
2. Description of the Related Art
There have heretofore been control systems in each of which, when the driving wheel of the motor vehicle has undergone a slip in the acceleration mode thereof, an engine output or a brake force is controlled to suppress the slip.
As the control system based on the engine output, for example, There have been a driving force control system for a motor vehicle as disclosed in the official gazette of Japanese Patent Application Laid-open No. 246335/1991. In this system, when the slip of the driving wheel has been detected, the driving force of the motor vehicle is controlled in such a way that, in order to reduce the engine output, the basic or fundamental fuel injection quantity is immediately corrected so as to cut the supply of fuel (to actualize "fuel-cut") under a condition which is predetermined for each cylinder in accordance with a slip ratio measured between a tire and a road surface.
In general, in the case where the fuel supply is cut, due to air which has passed through the cylinder subjected to the fuel-cut, unburnt gas emitted from any other cylinder is burnt within a catalyst. Accordingly, there is the problem that the temperature of the catalyst is liable to rise. Therefore, when the engine output control continues for a long time period, the damage of the catalyst is apprehended. Also in the system of Japanese Patent Application Laid-open No. 246335/1991, the fuel-cut control is interrupted for the protection of the catalyst when the catalyst temperature has reached a predetermined value.
Besides, in resetting the fuel supply operation from the fuel-cut mode, the so-called "resetting quantity increase" of the fuel is usually carried out to inject the fuel more than in the continuous injection mode of this fuel supply operation. Therefore, in the case where the number of cylinders to have the fuel cut off (hereinbelow, simply termed the "fuel-cut number" or "FCN") changes frequently, the fuel-cut and the reset are repeated frequently. This poses the problem that the temperature of the catalyst is more liable to rise.